1. Field of the Invention
The present invention relates generally to a wireless power transmitter, a method of controlling the same, and a temperature compensation method for a load value of the wireless power transmitter.
2. Description of the Related Art
Portable terminals such as mobile phones or PDAs (Personal Digital Assistants) are driven by rechargeable batteries due to their characteristics, and electric energy for charging is supplied to the batteries by using separate charging devices. Separate contact terminals are provided at outer sides of a charging device and a battery, which are electrically connected to each other by contacting the contact terminals.
However, in the contact type charging method, since the contact terminals protrude to the outside, they may be easily damaged or contaminated due to foreign substances, such as moisture, preventing the battery from being properly charged.
To solve this problem, recent wireless charging or noncontact charging technologies have been developed and are being utilized in many electronic devices.
These wireless charging technologies uses wireless power transmission, such as systems for automatically charging a battery only by positioning a mobile phone on a charging pad without connecting the mobile phone to a separate charging connector. Wireless electric toothbrushes or shavers are well known to many consumers as devices utilizing this technology. Since electronic products are wirelessly charged, their waterproof functions and portability are improved. Further development in the wireless charging-related technologies are expected to continue to significantly develop.
The wireless charging technologies largely include an electromagnetic induction method using coils, a resonance method using resonances, and a Radio Frequency (RF)/microwave radiation method of converting electric energy to microwaves to transfer the electric energy.
Although the electromagnetic induction method has been mainly used until now, as experiments of wirelessly transmitting electric power from a distance of several meters by using microwaves recently have been successfully performed in Korea and other countries, it is expected that all electronic products can be wirelessly charged anytime and anywhere in the near future.
The power transmission method using electromagnetic induction is a method of transmitting electric power between a first coil and a second coil. An induced current is generated if a magnet is moved in a coil, in which case a magnetic field is generated at a transmitting terminal and a current is induced at a receiving terminal according to a change in a magnetic field to produce energy. This phenomenon is called magnetic induction, and a power transmission method using magnetic induction shows optimum energy transmission efficiency.
As for the resonance method, Professor Soljacic of the Massachusetts Institute of Technology (MIT) announced in 2005 that electric power can be wirelessly transmitted from a charging device more than several meters away by using a resonance power transmission principle through a coupled mode theory. The wireless charging system of the MIT team uses a physical concept of resonance by which if a tuning fork is rung, a wine glass near the tuning fork is made to ring at the same frequency. The study team resonated electromagnetic waves containing electric energy instead of resonating sounds. Since the resonated electric energy is directly transferred only when a device having a resonance frequency exists and the unused parts do not spread out into the air but are reabsorbed as electromagnetic waves, the energy does not influence machines or human bodies unlike the other electromagnetic waves.
A wireless power transmitter may recognize nearby objects and perform an operation corresponding thereto. For example, a wireless power transmitter can measure the number of wireless power receivers located nearby, and accordingly, can adjust an amount of driving power output from the wireless power receivers.
However, a configuration of recognizing nearby objects by a conventional wireless power transmitter has not been discussed, and accordingly, there is a need in the art for a technology for a configuration of recognizing nearby objects.